In recent years, in order to observe the state of cerebral activity, optical brain function imaging devices have been developed to perform measurements conveniently and non-invasively using light. In such brain function imaging devices, near infrared beams of three different wavelengths λ1, λ2, and λ3 (for example, 780 nm, 805 nm, and 830 nm) are directed into the brain through light transmitting probes that are disposed on the head surface of the patient, and the strengths of the near infrared lights of the respective wavelengths λ1, λ2, and λ3 emitted from the brain (received brightness information) A(λ1), A(λ2), and A(λ3) are detected through light receiving probes disposed on the head surface.
Given this, a system of equations, shown in the exemplary system of equations (1), (2), and (3), is created using, for example, the Modified Beer Lambert method, in order to solve for the integral, along the length of the optical path, of the oxyhemoglobin (oxyHb) within the cerebral blood flow, and the integral, along the length of the optical path, of the deoxyhemoglobin concentration (deoxyHb) (referencing, for example, non-Patent Citation 1) from the light receiving intensity information A(λ1), A(λ2), and A(λ3). Moreover, from the integral, along the length of the optical path, of the oxyhemoglobin concentration (oxyHb) and the integral, along the length of the optical path, of the deoxyhemoglobin concentration (deoxyHb), the integral, along the length of the optical path, of the total hemoglobin concentration ((oxyHb)+(deoxyHb)) is calculated.A(λ1)=EO(λ1)×[oxyHb]+Ed(λ1)×[deoxyHb]  (1)A(λ2)=EO(λ2)×[oxyHB]+Ed(λ2)×[deoxyHb]  (2)A(λ3)=EO(λ3)×[oxyHB]+Ed(λ3)×[deoxyHb]  (3)
Note that EO (λn) is a light absorption coefficient for the oxyhemoglobin for light at the wavelength of λm, and Ed (λm) is a light absorption coefficient for deoxyhemoglobin for light of the wavelength λm.
The relationship between the measurement location and the distance (the channel) between the light transmitting probe and the light receiving probe will be explained here. FIG. 11A is a cross-sectional diagram showing the relationship between the measurement location and a light transmitting probe and light receiving probe pair, where FIG. 11B is a plan view diagram of FIG. 11A.
The light transmitting probe 12 is pressed against a light transmitting point T on the head surface of the patient and the light receiving probe 13 is pressed against a light receiving point R on the head surface of the patient. Moreover, light is emitted from the light transmitting probe 12, and the light that is emitted from the head surface is received into the light receiving probe 13. Of the light that is emitted from the light transmitting point T on the head surface, that light that traverses a banana shape (a measuring region) arrives at the light receiving point R of the head surface. This makes it possible to obtain light reception brightness information A(λ1), A(λ2), and A(λ3) regarding the measurement location of the patient that is at a depth of L/2 that is one half of the distance of the line connecting the light transmitting point T to the light receiving point R through the shortest distance along the head surface of the patient, from, in particular, the midpoint M of the line L that connects the light transmitting point T and the light receiving point R of through the shortest distance along the head surface of the patient, within the measurement region.
Moreover, in this optical brain function imaging device, a near-infrared spectroscopic analyzer (referencing Patent Citation 1, for example), or the like is used in order to measure separately the oxyhemoglobin concentration integrated along the length of the optical path (oxyHb), the deoxyhemoglobin concentration integrated along the length of the optical path (deoxyHb), and total hemoglobin concentration integrated along the length of the optical path ((boxyHb)+(deoxyHb)) in relation to a plurality of measurement locations within the brain.
FIG. 12 is a block diagram illustrating one example of a schematic structure for a conventional near-infrared spectroscopic analyzer. Moreover, FIG. 13 is a perspective diagram illustrating one example of the external appearance of the near-infrared spectroscopic analyzer illustrated in FIG. 12. Note that for ease of understanding, the plurality of optical fibers for light transmission and plurality of optical fibers for light reception, and the like, are omitted.
The near-infrared spectroscopic analyzer 201 has a case 211 that is of a rectangular-solid shape (for example, 70 cm×100 cm×120 cm).
A light source driver 202 for emitting light, an photodetector 203 for detecting light, an A/D converter 5, a controller 21 for light transmission/reception, a controller 22 for analysis, and a memory 23 are provided within the case 211, and 16 light transmitting probes 12, 16 light receiving probes 13, 16 light transmission optical fibers 14, 16 light reception optical fibers 15, a display device 226, and a keyboard 227 are provided outside of the case 221.
The light source driver 202 is a light source for the transmission of light to the various light transmitting probes 12 depending on driving signals inputted from the light transmission and reception controller 21, and is, for example, semiconductor lasers LD1, LD2, and LD3, or the like, which are able to emit near-infrared light of, for example, three different wavelengths λ1, λ2, and λ3.
The photodetector 203 is a detector, for example, a photoelectron multiplying tube, or the like, for detecting the respective near-infrared lights received by the individual light receiving probes 13, and outputting to the light transmission and reception controller 21 16 light reception signals (light reception brightness information) A(λ1), A(λ2), and A(λ3) through the A/D converters 5.
The light transmission optical fibers 14 and the light reception optical fibers 15 each have a cylindrical shape with respective diameters of 2 mm and lengths between 2 m and 10 m, and are able to transmit the near-infrared light in the axial direction thereof, where near infrared light that enters in from one end portion passes through the interior thereof to be emitted from the other end portion, and where near-infrared light that enters in from the other end portion passes through the interior thereof to be emitted from the one end portion.
Moreover, for a single light transmission optical fiber 14, a single light transmitting probe 12, and individual semiconductor lasers LD1, LD2, and LD3 of the light source driver 202, are connected to the end portions thereof, separated by a set length (between 2 m and 10 m). Moreover, for a single light reception optical fiber 15, a single light receiving probe 13 and a single photoelectron multiplier tube of the photodetector 203 are connected to the end portions thereof, separated by the set length (between 2 m and 10 m).
In this near-infrared spectroscopic analyzer 201, a holder 130 is used to cause the 16 light transmitting probes 12 and the 16 light receiving probes 13 to contact the head surface of the patient in a prescribed array. FIG. 14 is a plan view illustrating one example of a holder 130 into which the 16 light transmitting probes and the 16 light receiving probes have been inserted.
The light transmitting probes 12T1 through 12T16 and the light receiving probes 13R1 through 13R16 are disposed so as to alternate with four probes in the lateral direction and eight probes in the crosswise direction, with constant spacing between the light transmitting probes 12 and the light receiving probes 13, to obtain, from the head surface, light reception brightness information A(λ1), A(λ2), and A(λ3) for a specific depth from the head surface. Note that the spacing between probes is known as a “channel,” where typically 30 mm is used for the channel, where, if the channel is 30 mm, then the light reception brightness information A(λ1), A(λ2), and A(λ3) for a depth of between about 15 mm and 20 mm from the midpoint of the channel is envisioned. That is, light reception brightness information A(λ1), A(λ2), and A(λ3) related to cerebral activity is obtained essentially corresponding to the position on the surface of the brain, at a position that is between 15 mm and 20 mm deep from the head surface.
Note that the various through holes are assigned different codes (T1, T2, . . . , R1, R2, . . . ) so as to identify the type of light transmitting probe 12T1 through 12T16 or light receiving probe 13R1 through 13R16 that is at each through hole of the holder 130, and the individual light transmitting probes 12T1 through 12T16 are also assigned respective unique codes (T1, T2, . . . ) and the individual light receiving probes 13R1 through 13R16 are also assigned respective unique codes (R1, R2, . . . ). As a result, the individual light transmitting probes 12T1 through 12T16 and the individual light receiving probes 13R1 through 13R16 are each inserted into the respective through holes with the corresponding codes.
Moreover, the curvature of the head surface of the patient will vary depending on gender, age, and individual differences. Thus, in order to enable easy compatibility even when there are differences in curvature of the head surface, a holder 130 is used wherein the holders for holding the light transmitting probes 12T1 through 12T16 and the light receiving probes 13R1 through 13R16 are disposed in a grid shape on the head surface, where the holders are connected together by connectors that exhibit flexibility, and wherein there is rotational variability of the connectors, rotating around the holders, within a prescribed angle (referencing, for example, Patent Citation 2).
Furthermore, in the location relationships between these 16 light transmitting probes 12T1 through 12T16 and these 16 light receiving probes 13R1 through 13R16 it is necessary to adjust the timing of illumination with light from the light transmitting probes 12 and the timing of reception of light by the light receiving probes 13 so that light which is emitted from only a single light transmitting probe 12 will be received by a single light receiving probe 13, without simultaneously receiving light emitted by a plurality of light transmitting probes 12. Because of this, a control table that indicates the timing for emitting light, by the light source driver 202, and timing for detecting light, by the photodetector 203, is stored in the memory 23.
The light transmission and reception controller 21 outputs, to the light source driver 202, a signal for driving the transmission of light to a single light transmitting probe at a prescribed time, based on the control table that is stored in the memory 23, and also detects, through the photodetector 23, the reception signal (light reception brightness information) for the light received by the light receiving probe 13. The result, when shown in a plan view as illustrated in FIG. 14, is the collection of a total of 52 (S1 through S52) light reception brightness information A(λ1), A(λ2), and A(λ3).
Given this, the analysis controller 22 uses the system of equations (1), (2), and (3), to calculate the integral of the oxyhemoglobin concentration along the length of the optical path (oxyHb), the integral of the deoxyhemoglobin concentration along the length of the optical path (deoxyHb), and the integral of the total hemoglobin concentration along the length of the optical path ((oxyHb)+(deoxyHb)) (measurement data) based on the total of 52 light reception brightness information A(λ1), A(λ2), and A(λ3).